Phoebe figured that she had played the dumb game long enough. If tonight had strengthened anything, it was the doubts in her mind which she had about her family. Before rebirth, she had been the good daughter that always did as her parents asked and the things that were happening now did not happen then.
She never got to see the extremes to which her parents adored Ruth to the point of dying for her voluntarily in a dangerous situation. Phoebe figured either she wasn't their biological daughter or Ruth was their real daughter. There was also a possibility that maybe she was their daughter but so was Ruth and somehow she ended up with the Mayfairs.
It could also be that all three of those things were true. The one possibility she didn't even consider was that maybe she was a Mayfair. This was because the Mayfairs had black or blonde hair. Her red hair did not fit in with their family's physical appearance.